1. Field of the Invention
The present invention relates to a display device and a method for luminance adjustment of a display device, and can be applied to e.g. a liquid crystal display device. The present invention is to allow effective avoidance of image quality deterioration although an ambient light sensor for detection of the ambient light amount is provided in the effective pixel area, by correcting hue change due to an aperture ratio decrease accompanying the provision of the ambient light sensor by use of a hue correction mechanism.
2. Description of the Related Art
Among various kinds of display devices such as liquid crystal display devices, ones in which luminance adjustment is carried out depending on the ambient light amount have been provided. In particular, in some portable liquid crystal display devices such as electronic still cameras and cellular phones, the luminance of the display screen is adjusted through control of the luminance of the backlight to thereby ensure the visibility and reduce the power consumption, as disclosed in e.g. Japanese Patent Laid-Open No. Hei 11-295692.
In a related-art liquid crystal display device of this kind, the ambient light amount is detected by an ambient light sensor as a light-receiving element that receives ambient light. A configuration in which this ambient light sensor is provided in a liquid crystal display panel is disclosed in e.g. Japanese Patent Laid-Open No. 2007-322830.
FIG. 20 is a plan view showing a liquid crystal display panel applied to the liquid crystal display device of this kind. A liquid crystal display panel 1 includes an effective pixel area 2 formed by arranging sub-pixels in a matrix and displays various kinds of images by this effective pixel area 2. Furthermore, in the liquid crystal display panel 1, a light-blocking area 3 with a certain width is so formed as to surround this effective pixel area 2, so that the effective pixel area 2 is rimmed with a black frame formed of this light-blocking area 3. In the liquid crystal display panel 1, various drive circuits for driving the sub-pixels in the effective pixel area 2 are provided in this light-blocking area 3 and a peripheral area 4 around this light-blocking area 3. Moreover, in the liquid crystal display panel 1, e.g. a certain part along predetermined-one side is used as an area AR of external lead-out terminals, and power and so on is provided from the external lead-out terminals in this area AR.
FIG. 21A is an enlarged plan view of the peripheral part of the effective pixel area 2 indicated by symbol A in FIG. 20, and FIG. 21B is a sectional view along line B-B in this plan view. In the liquid crystal display panel 1, a liquid crystal 7 is sandwiched between a TFT (thin film transistor) substrate 5 and a CF substrate 6. The TFT substrate 5 is formed by providing, over a glass substrate 10 as a transparent insulating substrate, transistors 8 as thin film transistors (TFTs) included in red, green, and blue sub-pixels PXR, PXG, and PXB, hold capacitors Cs, pixel electrodes, an alignment film, and so on together with an ambient light sensor 9, signal lines SIG, scan lines SCN, and so on. The CF substrate 6 is formed by providing, over a glass substrate 11 as a similar transparent insulating substrate, a counter electrode, an alignment film, red, green, and blue color filters CFR, CFG, and CFB, and so on together with a light-blocking film 12 serving as the light-blocking area 3.
In the liquid crystal display panel 1 of the related art, the ambient light sensor 9 is provided at a position adjacent to the effective pixel area 2, in the light-blocking area 3. Furthermore, in the liquid crystal display panel 1, a sensor circuit 14 that is close to the ambient light sensor 9 and processes the output signal of the ambient light sensor 9 is provided in the light-blocking area 3. As the ambient light sensor 9, any of various photodetectors such as phototransistors and photodiodes is used. For the ambient light sensor 9, a light-blocking film 15 that blocks light from the backlight is provided on the glass substrate 10 side thereof. An aperture 12A that allows the incidence of ambient light on the ambient light sensor 9 is formed in the light-blocking film 12 on the CF substrate 6.
Used as the sensor circuit 14 is e.g. an integrating circuit that integrates the output signal of the ambient light sensor 9 with certain time interval and certain integration time in synchronization with the operation of the effective pixel area 2. In the related-art liquid crystal display panel 1, the output signal of the sensor circuit 14 is input to an external circuit, and the backlight is so controlled by this external circuit that the light amount of the backlight increases as the ambient light amount increases.
As shown in FIGS. 22A and 22B based on comparison with FIGS. 21A and 21B, in a liquid crystal display panel 21 as one of other proposed liquid crystal display panels of this kind, a correction sensor 9A is further provided and the light-reception result by the ambient light sensor 9 is corrected by the output signal of this correction sensor 9A. The correction sensor 9A has the same configuration as that of the ambient light sensor 9, except that the correction sensor 9A is prevented from receiving light from the backlight and ambient light. Specifically, a light-receiving element having substantially the same characteristics as those of the ambient light sensor 9 is used as the correction sensor 9A. More specifically, a light-receiving element having the same configuration, shape, and size as those of the ambient light sensor 9 is disposed adjacent to the ambient light sensor 9. The correction sensor 9A is so configured as to be prevented from receiving ambient light besides light from the backlight. Specifically, the correction sensor 9A is provided with a light-blocking film 15A that blocks light from the backlight similarly to the ambient light sensor 9. In addition, the whole of the correction sensor 9A is covered by a light-blocking component 15B so that it may be prevented from receiving light through the aperture 12A.
In this liquid crystal display panel 21, a sensor circuit 24 is provided instead of the sensor circuit 14. The sensor circuit 24 subtracts the output signal of the correction sensor 9A from the output signal of the ambient light sensor 9, to thereby prevent the light-reception result from changing due to dark current of the ambient light sensor 9. This subtraction processing for the output signal may be executed before the integration processing for the output signal of the ambient light sensor 9. Alternatively, it may be executed after integration of the output signal of the correction sensor 9A and the integration processing for the output signal of the ambient light sensor 9.
As shown in FIGS. 23A and 23B based on comparison with FIGS. 20 and 21A and 21B, in a display device 31 of the related art, a rectangular aperture 32A is formed in a case 32, and the liquid crystal display panel 1 or 21 is disposed inside this case 32 in alignment with the aperture 32A. In the display device 31, the size of the aperture 32A is so designed as to ensure the following states: the effective pixel area 2 is visible through the aperture 32A; ambient light enters the ambient light sensor 9 through the aperture 32A; and the peripheral area 4 around the light-blocking area 3 and the area AR of the external lead-out terminals are covered and hidden by the case 32. In addition, a guide or the like that defines the mounting position of the liquid crystal display panel 1 or 21 is provided.
Consequently, in the display device 31, the effective pixel area 2 is disposed inside the aperture 32A in such a manner as to be rimmed with a black frame that is formed of a part of the light-blocking area 3 and has a certain width D.